(1) Field of Invention
The present invention relates to a distributed sensor array, and more particularly to a system and method to enable a distributed group of sensors to cooperatively determine which sensor nodes in the group are closest to the source of a disturbance.
(2) Description of Related Art
There are a number of methods that have been developed for monitoring object presence and movement. However, many of these methods are limited in scope and are related to a narrow application, or require sophisticated sensors and centralized processing.
For example, U.S. Pat. No. 6,195,020, entitled, “Vehicle Presence Detection System,” describes a method that provides for detecting the presence of a vehicle within the protected area of a four-gate railroad crossing, and determining its location and direction of motion. However, this method is tailored to a narrow application and uses centralized processing.
Kalman filters are often used in object tracking. However, using Kalman filters requires sophisticated sensor systems and generally centralized processing. As an example, the method in U.S. Pat. No. 6,311,129, entitled, “Positioning Process and System Thereof,” makes use of a Kalman filter that processes the all-available measurements of a global positioning system.
There are also existing methods for tracking objects tagged with a specialized transmitting device. For example, the method in U.S. Pat. No. 6,154,139, entitled, “Method and System for Locating Subjects within a Tracking Environment,” tracks objects that are tagged with a badge that transmits radio-frequency (RF) and infrared (IR) signals. This method relies on the line-of-sight aspects of the IR transmissions in order to localize the objects being tracked.
In a related work, U.S. Pat. No. 5,119,104, discloses a radio-location system for multi-path environments, such as for tracking objects in a facility. This system includes an array of receivers distributed within the tracking area, coupled to a system processor over a local area network (LAN). A transmitter located with each tracked object transmits, at selected intervals, spread-spectrum transmissions including at least a unique identifier (ID). Object location is accomplished by time-of-arrival (TOA) differentiation. In a low-resolution embodiment, each receiver of the array is assigned a specific location-area, and receives transmissions almost exclusively from objects located in that area, thereby eliminating the need for any time-of-arrival circuitry. In this system, data from all sensors must be collected at a central system processor for localization analysis.
Another related invention is described in U.S. Pat. No. 6,208,247, entitled, “Wireless Integrated Sensor Network using Multiple Relayed Communications.” The patent relates to the remote detection, monitoring or tracking of vehicles, personnel, or other physical conditions. However, the patent is specifically concerned with hardware and communication protocols. It describes a highly integrated, miniature electronic sensing station that is specially adapted for use with other such sensing stations in a wireless, communicating network.
Other methods have been developed for motion prediction in a sensor array. These methods are concerned with predicting the future movement of a detected object and activating sensor nodes that may lie on the anticipated path of the moving object. In such methods, it is assumed that the moving object will only be detected within some limited range of the sensors, and therefore, only those sensor nodes closest to the moving object will detect it. Consequently, these methods do not specifically deal with the localization of objects that are potentially detected by many sensors at once.
The prior art in this area has generally relied on centralized processing of data from multiple sensors, or on limited range and line-of-sight properties of sensors to permit localization of sensed objects. Thus, a continuing need exists for a system using a distributed group of sensors to cooperatively determine which sensor nodes in the group are closest to the source of a disturbance, and for a system that requires no a priori knowledge of transmission intensity and allows for consistent activation of an exact number of nodes.